Michael Schmitt

Heinrich-Heine-Universität Düsseldorf | HHU · Institute of Physical Chemistry

The properties of the three lowest singlet electronic states (ground, (1)L(b), and (1)L(a) states) of indole (C(8)H(7)N) have been calculated with second-order approximate coupled-cluster theory (CC2) within the resolution-of-the-identity approximation. Refined electronic energies at the CC2 optimized structures and transition dipole moments were c...

High-resolution electronic spectra of indole (C(8)H(7)N) and their detailed analysis are reported. Thirteen low-lying vibronic bands--from the electronic origin transition at 35,231.4 cm(-1) up to 1000 cm(-1) above--are recorded with rotational resolution. Besides inertial parameters and inertial defects these spectra yield detailed information, fo...

The conformational space of tryptamine has been thoroughly investigated using rotationally resolved laser-induced fluorescence spectroscopy. Six conformers could be identified on the basis of the inertial parameters of several deuterated isotopomers. Upon attaching a single water molecule, the conformational space collapses into a single conformer....

The photophysics of 2-cyanoindole (2-CI) in solution (water, 2,2,2-trifluoroethanol, acetonitrile‚ and tetrahydrofuran) was investigated by steady-state as well as time resolved fluorescence and absorption spectroscopy. The fluorescence quantum yield of 2-cyanoindole is strongly sensitive to the solvent. In water the quantum yield is as low as 4 ....

The geometry changes of the tgt- and the ttt-rotamer of 1,2-diphenoxyethane were determined from a combined fit of line intensities in fluorescence emission spectra, obtained via pumping different vibronic transition, and the changes of rotational constants upon electronic excitation, which were taken from [E. G. Buchanan, P. S. Walsh, D. F. Plusqu...

The rotationally resolved electronic spectrum of the S1←S0 electronic origin band of 6-methylindole (6-MI) has been measured in a molecular beam and has been fit to rigid asymmetric rotor Hamiltonians in both electronic states using evolutionary strategies. Rotational constants, dipole moments in both electronic states, and orientation of the trans...

The structural changes of 1-(Phenylethynyl)naphthalene (1-PEN) upon excitation from the ground state to the lowest excited singlet state have been assessed from a combined Franck-Condon-Fit of fluorescence emission spectra after excitation of several vibronic bands of 1-PEN and ab initio calculations. An analysis of the infrared spectrum, the laser...

Vibronic couplings between the two lowest excited singlet states of the neurotransmitter serotonin are studied both experimentally and theoretically. Using rotationally resolved electronic spectroscopy, we observe a mode-dependent rotation of the S1 transition dipole moment (TDM). This is rationalized as a coupling of the S1 (1Lb) to the S2 (1La) s...

The excited state dipole moment of the lowest excited singlet state of 2,3-benzofuran in ethylacetate solution is determined using thermochromic spectroscopy and compared to the values, obtained for the isolated molecule from electronic Stark spectroscopy (M.-L. Hebestreit, et al., J. Mol. Struct., 2020, 1210, 127992) and to the results of ab initi...

The permanent dipole moments of 2-cyanoindole (cyanoindole = CNI) in its ground and lowest excited singlet states have been determined from rotationally resolved electronic Stark spectroscopy under jet-cooled conditions. From the orientation of the transition dipole moment and the geometry changes upon electronic excitation the lowest excited singl...

The permanent dipole moments of 1-methylindole in its ground and lowest excited singlet ππ*-state have been determined using the method of thermochromic shifts of the absorption and fluorescence spectra and compared to ab initio calculated dipole moments. While ab initio theory predicts an excited state dipole moment, which nearly equals that of th...

Laser induced fluorescence and fluorescence emission spectra of 2-cyanoindole and the binary 2-cyanoindole-(H2O)1 cluster in a molecular beam were analyzed using a combination of Franck-Condon (FC) fits of the emission spectra and ab initio calculations. The structural changes upon electronic excitation to the lowest excited singlet state have been...

The geometry changes of two rotamers of 1,3-dimethoxybenzene were determined from a combined fit of line intensities in fluorescence emission spectra, obtained via pumping different vibronic transition and the changes of rotational constants upon electronic excitation. The so determined changes are compared to the results of ab initio approximate c...

The changes of the structure of 4-cyanoindole upon electronic excitation have been determined from a combined Franck-Condon and rotational constants fit. The geometry changes were fit to simultaneously reproduce the intensities of 72 lines in the fluorescence emission spectra, obtained via excitation of six different vibronic bands in the first exc...

The method basically combines the existing ideas of excited state dipole moment determination via thermochromic fluorescence spectroscopy with the determination of the solvent cavity volume via concentration dependent density measurements of the solution densities at different weight fractions. Additionally, the determination of the cavity volume i...

The rotationally resolved electronic spectra of the origin band of 2,3-benzofuran has been measured and analyzed. Using electronic Stark spectroscopy, the dipole moments in the ground and electronically excited state have been determined. From the values for the permanent dipole moments, the orientation of the transition dipole moment and from the...

The altered electron distribution after electronic excitation gives rise to structural changes of the heavy atom frame of aromatic molecules. These changes can be influenced by the nature of substituents as well as by their relative position in the aromatic ring. We determined the changes of the structure of 1,2-dimethoxybenzene upon electronic exc...

The excited state dipole moment of 2-[(4-methoxyphenyl)ethynyl]-3-(1-methyl-1H-indol-3-yl)-quinoxaline has been determined in ethyl acetate solution using the method of thermochromic shifts. Three different models have been tested and are compared to each other and to the results of ab initio calculations at the coupled cluster CC2/cc-pVTZ and SCS-...

We report the gas phase conformational preferences of laser desorbed Ala-Ala dipeptides probed by action spectroscopy using the IRMPD-VUV method. The molecules were internally cooled through collisional cooling in a supersonic jet environment. An IR spectrum was obtained experimentally in the spectral range of 700-1850 cm-1, and subsequently interp...

The structural changes of 1,2-dimethoxybenzene upon electronic excitation have been elucidated from a comparison of ab initio calculations and fits of the structural changes to experimental inertial parameters both in the basis of internal coordinates as well as in vibrational distortion coordinates. It is shown that the use of vibrational distorti...

In this paper we report the results of gas-phase IR spectroscopy of neutral glycylglycine (Gly-Gly) in the 700-1850 cm⁻¹ frequency range. A combination of laser desorption, jet-cooling, and IR multiple-photon dissociation vacuum-ultraviolet (IRMPD-VUV) action spectroscopy is employed, together with extensive quantum-chemical calculations that assis...

The rotationally resolved electronic Stark spectrum of 4-cyanoindole and some N-D and C-D deuterated isotopologues has been measured and analyzed.

We present the temperature dependent density, fluorescence emission and absorption spectroscopic data, that are needed for an evaluation of the excited state dipole moment of anisole in ethyl acetate via the methods of thermochromic shifts. Furthermore, the rotationally resolved electronic Stark spectrum of anisole in the molecular beam is presente...

The rotationally resolved electronic spectra of the origin bands of 3-cyanoindole, cyanoindole(d1), and the 3-cyanoindole-(H2O)1 cluster have been measured and analyzed using evolutionary algorithms. For the monomer, permanent dipole moments of 5.90 D for the ground state, and of 5.35 D for the lowest excited singlet state have been obtained from e...

The excited state dipole moment of anisole has been determined in the gas phase from electronic Stark spectroscopy and in solution using thermochromic shifts in ethyl acetate. Electronic excitation increases the anisole dipole moment in the gas phase from 1.26 D in the ground state to 2.19 D in the electronically excited singlet state, leaving the...

Light driven changes of molecular dipole moments are vital for the understanding of solvent reorientation or relaxation of a solute, or the reorientation of the local protein surrounding of electronically excited aromatic amino acids. Furthermore, explication of resonance energy transfer processes like Förster Resonant Energy Transfer (FRET) and mo...

Rotationally resolved electronic Stark spectra of different rotamers of 1,2-, 1,3-, and 1,4-dimethoxybenzene have been recorded and analyzed using evolutionary strategies. The experimentally determined dipole moments as well as the transition dipole moments are compared to the results of \textit{ab initio} calculations. For the electronic ground st...

Conformational assignments in molecular beam experiments are often based on relative energies, although there are many other relevant parameters, such as conformer-dependent oscillator strengths, Franck-Condon factors, quantum yields and vibronic couplings. In the present contribution, we investigate the conformational landscape of 1,3-dimethoxyben...

We present fluorescence emission spectra of the 2-tolunitrile dimer and the 2-tolunitrile water cluster through various vibronic bands in the electronically excited state. From the transition dipole moments in the individual monomers, the 2-TN dimer has shown to form J-aggregates, which is why the one-photon allowed transition is the S1 state in th...

The lowest two electronically excited singlet states of indole and its derivatives are labelled as La or Lb states, based on the orientation of the transition dipole moment (TDM) and the magnitude of the permanent electric dipole moment. Rotationally resolved electronic Stark spectroscopy in combination with high level ab initio calculations offers...

We present far infrared spectra of the conformer A of tryptamine in the 200 to 500 cm(-1) wavenumber range along with resonant photoionization spectra of the far-infrared excited conformer A of tryptamine. We show that single-far-infrared photon excited tryptamine has highly structured resonance enhanced multi-photon ionization spectra, revealing t...

Conformational preferences are determined by (de-)stabilization effects like intramolecular hydrogen bonds or steric hindrance of adjacent substituents and thus, influence the stability and reactivity of the conformers. In the present contribution, we investigate the conformational landscape of 3-methoxyphenol using a combination of high resolution...

The estimate of the magnitude and the orientation of molecular electric dipole moments from the vector sum of bond or fragment dipole moments is a widely used approach in chemistry. However, the limitations of this intuitive model have rarely been tested experimentally, especially for electronically excited states. In the present study we find rules...

The 5-hydroxytryptamine receptors (5HTn) are optimized for 5-hydrotryptamine molecules, resulting in a significantly enhanced psychoactive response compared with the 4-, 6-, 7-isomers. This is despite their relatively similar energetic stabilities, excited state lifetimes and emission characteristics. In this work we investigate the conformational...

We determined the changes of the geometries of 2- and 3-tolunitrile upon excitation to the lowest excited singlet states from Franck-Condon fits of the vibronic intensities in several fluorescenceemission spectra and of the rotational constant changes upon excitation. These structural changes can be connected to the altered electron distribution in...

The dipole moments of the ground and lowest electronically excited singlet state of 5-methoxyindole have been determined by means of optical Stark spectroscopy in a molecular beam. The resulting spectra arise from a superposition of different field configurations, one with the static electric field almost parallel to the polarization of the excitin...

Rotationally resolved fluorescence excitation spectra of the origin bands in the S1 ← S0 transition of 2-tolunitrile (2TN) and 3-tolunitrile (3TN) have been recorded in the collision-free environment of a molecular beam. Analyses of these data provide the rotational constants of each molecule and the potential energy curves governing the internal r...

The molecular structures of guaiacol (2-methoxyphenol) and mequinol (4-methoxyphenol) have been studied using high resolution electronic spectroscopy in a molecular beam and contrasted with ab initio computations. Mequinol exhibits two low frequency bands that have been assigned to electronic origins of two possible conformers of the molecule, tran...

The geometry change of 5-cyanoindole upon electronic excitation from the ground to the lowest excited singlet state has been determined from a combined fit of the rotational constant changes upon excitation and the vibronic intensities in various fluorescence emission spectra using the Franck-Condon principle. The so determined geometry change is c...

Rotationally resolved electronic spectra of seven vibrationally excited bands in the electronic spectrum of benzimidazole have been measured and analyzed. From the vibrational contributions to the rotational constants, an assignment of the hot bands could be made on the basis of anharmonic corrections to the harmonic normal modes and by using the i...

The rovibronic spectra of two bands of 5-cyanoindole at 348 and 884 cm-1 have been measured and analyzed using a rigid rotor Hamiltonian. A vibrational assignment could be given on the basis of an anharmonic analysis of the vibrational spectrum of 5-cyanoindole making use of the information of the vibrationally averaged rotational constants. Strong...

Vibronic spectra of 9H-adenine, 9-acetyladenine and several alkyladenines have been recorded by resonant two-photon ionization spectroscopy of the laser-desorbed molecules, entrained in a molecular beam. While adenine and the alkyladenines exhibit similar electronic spectra, 9-acetyladenine behaves considerably different. Theoretical absorption spe...

The structures of syn and anti 6-methoxyindole have been determined in the electronic ground and excited states using rotationally resolved electronic spectroscopy and high level ab initio calculations. Second order coupled cluster theory predicts the lowest excited singlet states to be heavily mixed and the transition dipole moments to depend stro...

The structure and electronic properties of the electronic ground state and the lowest excited singlet state (S(1) ) of 5-fluoroindole (5FI) were determined by using rotationally resolved spectroscopy of the vibration-less electronic origin of 5FI. From the parameters of the axis reorientation Hamiltonian, the absolute orientation of the transition...

The electronic origin bands A and B of 5-hydroxyindole were measured using rotationally resolved electronic spectroscopy. From comparison of the experimental rotational constants to the results of ab initio calculated structures, we could make the assignment of band A being due to the syn conformer and of band B being due to the anti conformer. The...

The structure and electronic properties of the electronic ground and the lowest excited singlet states of 5-cyanoindole (5CI) were determined using rotationally resolved spectroscopy of the vibrationless electronic origin of 5CI. In contrast to most other indole derivatives, the lowest excited state of 5CI is determined to be of L(a) character. The...

The usefulness of an evolutionary algorithm (EA) based approach to the automated evaluation of molecular parameters from various kind of spectra is shown. The applicability of the method ranges from rotationally resolved electronic spectroscopy of large molecules to nuclear magnetic resonance (NMR) spectroscopy of molecules, which are partially ori...

We measured the rotationally resolved electronic spectra of the origin and of three vibronic bands of 1,4-benzodioxan. From comparison to various ab-initio-calculated structures of 1,4-benzodioxan, the twisted C(2) symmetric 1,4-benzodioxan was shown to be responsible for all the observed spectral features. We analyzed the inertial defects in both...

The rotationally resolved electronic spectrum of tetrahydrocarbazole seeded in a molecular beam has been taken. The lowest excited singlet state of tetrahydrocarbazole could be shown to have L(a) character, in contrast to nearly all other indole derivatives, which have the L(b) as lowest state. An upper limit for the energy difference of both state...

A remarkable influence of the orientation of a polar side chain on the direction of the S(1) ← S(0) transition dipole moment of monosubstituted benzenes was previously reported from high-resolution electronic spectroscopy. In search for a more general understanding of this non-Condon behavior, we investigated ethylamino-substituted indole and benze...

Rotationally resolved electronic spectra of the vibrationless origin and of eight vibronic bands of 5-methoxyindole (5MOI) have been measured and analyzed using an evolutionary strategy approach. The experimental results are compared to the results of ab initio calculations. All vibronic bands can be explained by absorption of a single conformer, w...

The FTIR spectrum of pyrazine in the gas phase has been measured and analyzed using automated evolutionary algorithms. For the stronger bands, the rotational constants for ground and vibrationally excited states, the correct band types and in some cases centrifugal distortion constants could be extracted. Several hot hands have been identified and...

The rotationally resolved spectrum of the o-toluidine S(1)<-- S(0) origin was measured using laser induced fluorescence spectroscopy. From the resulting spectrum torsional barriers to internal rotation of the methyl group were derived, which resulted in S(0) state values of V(3) = 699 +/- 11 cm(-1) and V(6) = 64 +/- 11 cm(-1) with an effective rota...

The structures of the van der Waals bonded complexes of phenol with one and two argon atoms have been determined using rotationally resolved electronic spectroscopy of the S(1)<--S(0) transition. The experimentally determined structural parameters were compared to the results of quantum chemical calculations that are capable of properly describing...

Rotationally resolved electronic spectra of three different conformers of 5-methoxytryptamine were recorded in a molecular beam. 5-Methoxy substitution reduces the number of observed conformers to three compared to seven that have been reported for tryptamine. Quantum chemical calculations indicate that anti-rotamers of the methoxy-group are more s...

The vibronic spectrum of tryptamine has been studied in a molecular beam up to an energy of 930 cm(-1) above the S(0)-S(1) electronic origin. Rotationally resolved electronic spectra reveal a rotation of the transition dipole moment direction from (1)L(b) to (1)L(a) beginning about 400 cm(-1) above the (1)L(b) origin. In this region, vibronic bands...

The relative fluorescence intensities of three conformers of tryptamine have been determined as a function of stagnation pressure and nozzle temperature in a supersonic expansion. The relative intensities of the conformers that are connected by different direct and indirect interconversion paths on the potential-energy hypersurface differ considera...

Room-temperature absorption spectroscopy of the A∼1A2←X∼1A1 transition of formaldehyde has been performed in the 30140–30790 cm−1 range allowing the identification of individual lines of the 201403 and 202401 rovibrational bands. Using tunable ultraviolet continuous-wave laser light, individual rotational lines are well resolved in the Doppler-broa...

Five different isotopologues of the benzoic acid dimer and a vibronic band located 57 cm(-1) above the electronic origin, which is assigned to the out-of-plane butterfly motion, are studied by rotationally resolved UV spectroscopy. From these measurements a ground-state structure with C(2h) symmetry is deduced, whereas the symmetry is lowered to C(...